Patent Issued for Computationally-Efficient Equalization in Polmux OFDM Transmission with Direct Detection via Joint Transmitter and Receiver Processing
Patent number 8615171 is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "It is anticipated that the transport capacity of next-generation optical access/metro networks (
"As a result of its high spectral efficiency, resilience to linear dispersion, and efficient digital signal processing (DSP)-based implementation, optical orthogonal frequency division multiplexing (OFDM) has emerged as an attractive candidate for next-generation fiber-optic systems. Moreover, optical OFDM-based Multiple Access (OFDMA) is particularly attractive for next-generation optical access/metro systems due to its application transparency and bandwidth flexibility.
"Polarization-multiplexed (POLMUX) OFDM transmission with direct (non-coherent) detection has been shown to further increase spectral efficiency at ultra high-speeds while advantageously requiring a reduced optical receiver complexity and cost. By achieving record 40.sup.+ Gb/s data rates with simplified optical receivers, POLMUX-OFDMA with direct detection (DD) is a highly-promising technology for future fiber-based access/metro systems.
"However, while POLMUX-OFDM-DD systems reduce receiver complexity compared to coherent receivers, they also increase the complexity of the required post-photodetection electronic digital signal processing (DSP). More particularly--and due to direct detection--cross-polarization interference will occur in the optical receiver, which must be corrected, or equalized, in post-photodetection DSP. Operationally, this DSP-based equalization requires both the computation of a 4.times.4 matrix inverse and the multiplication of incoming data with the inverted matrix (i.e. data equalization). Consequently, both of these steps can prohibitively increase DSP receiver complexity and, if performed in a sub-optimal way, can also enhance noise effects.
"Previously, we have proposed receiver-end processing algorithms that can notably reduce the complexity of the 4.times.4 matrix inverse computation. However, the computational complexity of the equalization step remained unchanged. Since the equalization step must be performed significantly more often than the required matrix inversion, it subsequently became a limiting factor in overall computational complexity. Moreover, in our previous work, the equalization step was performed sub-optimally with respect to theoretically-optimal maximum likelihood (ML) equalization, which can enhance noise effects and degrade the bit error rate (BER) of the system. Consequently, a processing algorithm that enables computationally-efficient ML equalization and reduces overall complexity would represent a significant advancement in the art as it pertains to high-speed, real-time POLMUX-OFDM-DD systems."
In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "An advance is made in the art according to an aspect of the present disclosure directed to a method for joint transmitter and receiver processing to achieve computationally efficient as well as maximum likelihood (ML) equalization in polarization multiplexed (POLMUX) orthogonal frequency division multiplexed (OFDM) transmission with direct detection.
"Accordingly, the present disclosure is directed to joint transmitter and receiver-end digital signal processing methods for POLMUX-OFDM-DD systems which exploiting variants of a fundamental block-symmetric (B-S) structure in the channel estimation matrix that is used in equalizing cross-polarization interference. Specifically, the method enables: i.) theoretically-optimal maximum likelihood (ML) equalization or optimized linear equalization with minimal computational complexity; ii.) two- and four-fold potential increases in reliability, as measured by the achievable diversity order; and iii.) full channel state information feedback with minimal overhead. Advantageously, each of these advantages can be exploited in high-speed, real-time POLMUX-OFDM-DD applications, such as OFDMA passive optical networks (PON).
"Advantageously, the method according to the present disclosure maintains spectral and cost efficiency of contemporary POLMUX-OFDM-DD systems, while both enabling theoretically-optimal maximum likelihood (ML) equalization with reduced computational complexity and increased reliability in high-speed (40.sup.+ Gb/s), real-time applications."
URL and more information on this patent, see: Cvijetic, Neda; Prasad, Narayan; Qian, Dayou; Wang, Ting. Computationally-Efficient Equalization in Polmux OFDM Transmission with Direct Detection via Joint Transmitter and Receiver Processing. U.S. Patent Number 8615171, filed
Keywords for this news article include: Electronics, Digital Signal Processing,
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